Ice is common in our solar system, from ice-covered moons and rings around distant Jupiter and Saturn to deposits at the poles of the Moon... and even Mercury! Obviously, ice is present on our own world, too. The only ice off-Earth that's easy to see distinctly is the Martian polar cap. Seeing it will take some magnification, though. Both of Mars' poles have water ice, but its south pole is coated with a layer of frozen carbon dioxide.

You can see many of these icy worlds when you view the Saturn system this month. Saturn reaches opposition on April 15 and is now visible earlier in the evening and all night long. Through a telescope you'll see the icy rings, Titan and -- with a little luck -- Enceladus. Saturn's moon Titan is famous for its methane, which can exist as a solid, a liquid and a gas at Titan's surface temperatures and pressures. But even Titan has water ice -- and hydrocarbon ice -- on its surface. Saturn's intriguing moon Enceladus actually spews water ice out of geyser-like vents, ice that orbits Saturn as the E ring! And Saturn's rings themselves are made up mostly of water ice.

Comets are made of ice and dust: frozen water ice and sometimes ice from other substances including methane, ammonia, carbon monoxide, sulfur and hydrogen sulfide.

The moons of the outer planets are rich in ice, too. Jupiter's moon Europa is blanketed by frozen water ice, with a liquid ocean under the ice blanket. Ganymede is the largest moon in our solar system, even larger than Mercury. It's mostly water ice with a rocky core. Callisto is rock and water ice, too, although ammonia and carbon dioxide ice may be present.

Uranus and Neptune are filled with 'icy' materials like water, ammonia and methane under incredible heat and pressure. Their moons are ice-rock conglomerates made mostly of water ice, with some ammonia and dry ice. Neptune's moon Triton even has volcano-like geysers that erupt nitrogen gas.

Mercury is easy to spot this month. And we say goodbye to Jupiter for a few months, but not before a pretty crescent moon pairing on April 22.